1. Field of the Invention
The invention relates to a laser system with a passively Q-switched laser, a spectrally widening element, and a compression element.
2. Description of the Related Art
Laser systems of this kind are intended to be utilized for generating ultra-short laser pulses. In prior art, only complicated mode-coupled laser systems are hitherto known which may achieve a pulse duration of under 10 ps. Hence a simple and compact solution to generate laser pulses in the sub-10 ps range offers a substantial market potential. A field of application, among others, is the highly-precise micro-material processing because a heat input in the material which is reduced by a short pulse duration offers quality advantage, e.g. more precise edges in laser cutting. Mode-coupled solid-state lasers known from prior art are hitherto used as typical sources for ps pulses. Apart from the active medium, they are comprised of a nonlinear switch, e.g. a saturable semiconductor mirror, and elements for dispersion compensation. These complex and alignment-sensitive free-beam structures furnish pulse sequence frequencies in a range from 10 MHz to greater than 100 MHz. However, purposive pulse sequence frequencies for most applications are those under 10 MHz, typically some 100 kHz. Therefore, with prior art mode-coupled solid-state lasers it is necessary to implement additional elements which reduce the pulse sequence frequency. Customary elements are so-called resonator-extending mirror arrangements which however increase the complexity of the structures still further and thus make these sensitive to alignments. Alternatively, a pulse picker (e.g. a Pockel cell) is implemented upstream to the amplifier stages which reduces the pulse sequence frequency into the range required for the application. On the whole, mode-coupled laser systems are always sensitive free-beam structures whereby they are only conditionally suitable for commercial use.
The passively Q-switched lasers according to the generic term of the present invention are simply built-up compact microchip lasers comprised of a monolithic compound structure consisting of a saturable absorber, a laser crystal, and a resonator mirror and are pumped with a laser diode through simple optics. In this manner, pulses with pulse sequence frequencies of several 10 kHz up to some MHz with pulse durations ranging between 50 ps and 200 ps can be generated. A pulse duration smaller than 10 ps with these passively Q-switched lasers has not yet been possible hitherto.